Process for lowering the iron content in nickel melts

ABSTRACT

A process for increasing the relative proportion of nickel in a nickel melt which originally contains as little as 20% nickel and the balance principally iron and non-metal contaminants, which comprise blowing a stream of oxygen mixed with a cooling agent into said melt through at least one double pipe tuyere, the oxygen and cooling medium being blown in through the center pipe and a stream of hydrocarbon being blown into the melt through the space between both of said pipes, the refining, cooling and protecting materials all being injected below the surface of said melt.

United States Patent 1191 Brotzmann et al.

PROCESS FOR LOWERING THE IRON CONTENT IN NICKEL MELTS Inventors:

Assignee:

Filed:

Appl. No.:

Karl Brotzmann; Hans Georg Fassbinder, both of Sulzbach-Rosenberg, Germany Eisenwerk-Gesellschaft Maximilianshutte mbl-l, Sulzbach-Rosenburg, Germany Mar. 29, 1974 Foreign Application Priority Data Mar. 30, 1973 Germany 2316110 US. Cl. 75/60; 75/52; 75/59 Int. Cl. C21C 5/34 Field of Search 75/59, 60, 52

References Cited UNITED STATES PATENTS 3,706,549 12/1972 Knuppcl 75/60 3,726,665 4/1973 Minnick 75/52 3,751,242 8/1973 Knuppel 75/60 3,771,998 11/1973 Knuppel 75/60 3,773,496 11/1973 Knuppel 75/60 Primary Examiner'Peter D. Rosenberg Attorney, Agent, or FirmLawrence 1. Field 5 7 ABSTRACT A process for increasing the relative proportion of nickel in a nickel melt which originally contains as little as 20% nickel and the balance principally iron and non-metal contaminants, which comprise blowing a stream of oxygen mixed with a cooling agent into said melt through at least one double pipe tuyere, the oxygen and cooling medium being blown in through the center pipe and a stream of hydrocarbon being blown into the melt through the space between both of said pipes, the refining, cooling and protecting materials all being injected below the surface of said melt.

7 Claims, No Drawings PROCESS FOR LowE Nc THE iRoN CONTENT IN NICKEL ELTs j I The invention relates to a process fordiminishingthe content of iron and other contaminants present in nickel melts containing over %nick el, by blowing a refining gas into the melt whileit is'in "a converter.

Nickel is of considerable significance as an alloying element in the metallurgy of iron; especially when melting high grade steels. it is frequently used as ferronickel which' is'requi'red'to contain 'a specific minimum content of nickel-.Therefore it is oftennecessar'y to increase the nickel content of nickelous pig iron or nickelous slag melts byremoving iron from the melts along with other undesired-elements such as carbon, silicon, phosphorus and sulfur which may 'be present in the melt.

This may be achieved for instance by blowing oxygen onto the nickelous iron melt whereby the iron and the.

other undesired elements are oxidized. in view of the relatively low nickel contents. of the,initial melt, in.

order to raise the nickelcontent appreciably, it -is necessary to achieve asubstantial diminution in the iron content, which is accomplished by oxidizing large amounts of iron. l-lo'wever such slagging of iron releases heat to such an extent that the life of a converter lining is seriously affected, "and furthermore the large contents of ferrous oxide in the slag at temperatures above l,650C will strongly attack the usual converter lining. Also, this oxidation of large amounts of iron is inevitably accomplished only by oxidizing a large percentage of the nickel, along with the iron.

The present invention is directed to a process for diminishing the iron content and the content of other undesired contaminations in nickel-iron melts, whereby the nickel content is raised appreciably by a procedure which does not jeopardize the converter lining.

The desired results are obtained by introducing a mixture of oxygen and of a cooling medium both surrounded by hydrocarbon, into the melt and below the bath surface. This is achieved, preferably by means of a double-pipe tuyeres wherein the mixture of oxygen and cooling medium passes through the center pipe while gaseous or liquid hydrocarbons, for instance natural gas, propane, methane, butane, light fuel oil, fuel oil or mixtures thereof pass through the annular gap between the two concentric pipes of said tuyeres. The tuyere pipes may be made of ordinary steel, copper or high grade steel. In a preferred embodiment of the invention, the oxygen supply pipe consists of stainless steel and the outer pipe of ordinary steel.

The hydrocarbons used in the process of the invention serve to protect the tuyeres and the surrounding converter masonry, so that there will be essentially an even burn-off of tuyeres and masonry. The percentage proportion of the cooling medium should be at least 50% by weight during the iron slagging or scorification phase since the cooling medium essentially is used principally to take up the large amounts of heat generated during iron slagging from the melt and slag and from the converter and so to avoid the harmful effects of such heat. This can be accomplished particularly effectively if the mixture of oxygen and cooling medium includes a decomposable coolant. For example, a mixture of 20% oxygen and 80% water vapor or carbon dioxide has been found particularly effective in the process.

The large amounts of the cooling medium ensure that, there will bethorough bath mixing, leading to rapid equalizationof concentration and henceto a reaction aproaching chemiealequilibrium. It is particulary advantageous to. use limestone dust as the cooling medium, since limestone is of high specific heat capacity andwill dissociate into carbon dioxide and lime endo-f thermallyjin the. melt. The carbon dioxide will then decompose endothermally in {the melt to carbon monoxide and oxygen, .calcium oxide being transferred into the slag and contributing to the formation of a highbasic slag which is compatible with the durability of the converter lining.

Loading limestone dust into the oxygen provides spatterless blowing; no foaming of the slag or ejection of slag or metal occurs, because the amount of gas introduced into the melt is significantly smaller. In addition the calcium oxide entering the melt after decomposition physically contributes to calming the refining process. Thus, while durability of the converter lining is being improved, there will also be short refining times and economical refining. Another economic benefit is that the refining slag, containing for'instance' 30% iron oxide and 50% calcium oxide, may be used when makingsteel or as a basic fluxing material in the blast furnace. I V v Preferably the amount of hydrocarbon will be not more than about 10% of the weight of the mixture of oxygen and cooling medium; since larger quantities frequentlylead to deposit formation at the tuyere tips and to wear of the tuyeres. However, because the cooling medium also contributes to protecting the tuyere mouths and the surrounding converter masonry, the quantity of hydrocarbon preferably will be raised or lowered depending on the proportion of cooling means in the mixture.

Refining in the process of the invention with respect to the nickel-iron melt first takes place with an oxygen stream containing only a minor amount of cooling medium, until the undesired non-metallic elements (C, Si, P, Etc.) have been eliminated and the temperature of the bath is of the order of l,600C. Ordinarily this stage will be reached within a few minutes, whereupon iron slagging will begin, during which the proportion of cooling medium in the mixture is increased to at least 50%, preferably 80%, and the amount of hydrocarbon is lowered down to 6-7% by weight, of the total mixture, or even less, and thus refining continues until the melt has reached its desired iron content.

By way of example, 5 tons of a nickel-iron melt of the following composition, in percent by weight,

iron Zl nickel 2 carbon 1.4 silicon (l. l() phosphorus 0.04 sulfur was charged at a temperature of l.300C into a 5-ton bottom blown converter. Five tuyeres, arranged in a circle each tuyere consisting of two concentric pipes with diameters of 12 and 22 mm respectively were disposed to extend through the converter bottom. During the first six minutes of refining, oxygen and limestone dust were injected into the melt at a rate of 2,000 standard cubic meters/hour and 4,000 kg/hour respectively, through the inside pipes and 3% by weight of propane (based on the weight of the mixture) was blown into the melt in the converter through the annular gap between the inner and outer tuyere pipes. Upon onset of iron slagging, the limestone rate in the oxygen was raised to 4Kg/std. m and simultaneously the proportion of hydrocarbon blown in around the mixture was reduced to 2% by weight. Refining was continued without further changes in proportions of limestone, oxygen or hydrocarbon, and the melt was tapped at a temperature of l,650C. Analysis of the refined melt showed:

59 iron 41 nickel carbon 0.004 phosphorus 0.010 sulfur The slag contained 52% of ferrous oxide, 45% of calcium oxide and only 3% of NiO. From this it will be seen that by practice of the process of the invention, it is possible to raise the nickel content of a nickelous iron melt, without sacrificing the nickel yield and without exceeding the permissible bath or slag temperatures.

Having now described a preferred embodiment of the invention it is not intended that it be limited except as may be required by the appended claims,

We claim:

1. in a process for diminishing the content of iron and other contaminants in iron-nickel melts containing more than of nickel, in which an oxygencontaining refining gas is blown into a converter, to oxidize the iron and other contaminants in said melt, thereby enriching the nickel content of the melt, the improvement which comprises:

blowing into said convertor a mixture of oxygen and cooling medium and a separate stream of hydrocarbon surrounding said mixture, said mixture and said hydrocarbon being blown into the converter beneath the bath surface,

wherein said cooling agent is a decomposable substance selected from the group consisting of limestone, water vapor and carbon dioxide and mixtures thereof.

2. A process as defined in claim 1, characterized in that the proportion by weight of the cooling medium in the mixture will amount to at least during the stage of the process in which iron is being oxidized.

3. A process as defined in claim 1, wherein cooling medium includes water vapor or carbon dioxide.

- 4. A process as defined in claim 1 wherein the mixture comprises oxygen loaded with limestone dust.

5. A process as defined in claim 1 wherein the hydrocarbon surrounds the mixture of oxygen and cooling medium concentrically.

6. A process as defined in claim 1 wherein the proportion of hydrocarbon does not exceed 10% by weight with respect to the mixture of oxygen and cooling medium.

' 7. A process as defined in claim 1 wherein the proportion of hydrocarbon is varied inversely in relation to the amounts of cooling medium in the mixture. 

1. IN A PROCESS FOR DIMINISHING THE CONTENT OF IRON AND OTHER CONTAMINANTS IN IRON-NICKEL MELTS CONTAINING MORE THAN 20% OF NICKEL, IN WHICH AN OXYGEN-CONTAINING REFINING GAS IS BLOWN INTO A CONVERTOR, TO OXIDIZE THE IRON AND OTHER CONTAMINANTS IN SAID MELT, THEREBY ENRICHING THE NICKEL CONTENT OF THE MELT, THE IMPROVEMENT WHICH COMPRISES: BLOWING INTO SAID CONVERTOR A MIXTURE OF OXYGEN AND COOLING MEDIUM AND A SEPERATE STREAM OF HYDROCARBON SURROUNDING SAID MIXTURE, SAID MIXTURE AND SAID HYDROCARBON BEING BLOWN INTO THE CONVERTOR BENEATH THE BATH SURFACE, WHEREIN SAID COOLING AGENT IS A DECOMPOSABLE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF LIMESTONE, WATER VAPOR AND CARBON DIOXIDE AND MIXTURES THEREOF.
 2. A process as defined in claim 1, characterized in that the proportion by weight of the cooling medium in the mixture will amount to at least 50% during the stage of the process in which iron is being oxidized.
 3. A process as defined in claim 1, wherein cooling medium includes water vapor or carbon dioxide.
 4. A process as defined in claim 1 wherein the mixture comprises oxygen loaded with limestone dust.
 5. A process as defined in claim 1 wherein the hydrocarbon surrounds the mixture of oxygen and cooling medium concentrically.
 6. A process as defined in claim 1 wherein the proportion of hydrocarbon does not exceed 10% by weight with respect to the mixture of oxygen and cooling medium.
 7. A process as defined in claim 1 wherein the proportion of hydrocarbon is varied inversely in relation to the amounts of cooling medium in the mixture. 